Electrodes (contacts) problems and methods of production of electrodes for electronic devices are widely discussed in scientific and technical literature.
The development of nanoscale MOSFETs has given rise to increased attention paid to the role of parasitic source/drain and contact resistance as a performance-limiting factor (see, Reinaldo Vega and, Tsu-Jae King Liu, “Advanced Source/Drain and Contact Design for Nanoscale CMOS”, Electrical Engineering and Computer Sciences University of California at Berkeley, Technical Report No. UCB/EECS-2010-84 http://www.eecs.berkeley.edu/Pubs/TechRpts/2010/EECS-2010-84.html, May 20, 2010). Dopant-segregated Schottky (DSS) source/drain MOSFETs have become popular in recent years to address this series resistance issue, since DSS source/drain regions comprise primarily of metal or metal silicide. The small source/drain extension (SDE) regions extending from the metallic contact regions are an important design parameter in DSS MOSFETs, since their size and concentration affect contact resistance, series resistance, band-to-band tunneling (BTBT), SDE tunneling, and direct source-to-drain tunneling (DSDT) leakage. Reinaldo Vega and, Tsu-Jae King Liu's work investigates key design issues surrounding DSS MOSFETs from both a modeling and experimental perspective, including the effect of SDE design on ambipolar leakage, the effect of random dopant fluctuation (RDF) on specific contact resistivity, 3D FinFET source/drain and contact design optimization, and experimental methods to achieve tuning of the SDE region.
C. Liu, V. Kamaev, and Z. V. Vardeny in “Efficiency enhancement of an organic light-emitting diode with a cathode forming two-dimensional periodic hole array”, APPLIED PHYSICS LETTERS, Vol. 86, p. 143501, (2005) describe fabrication of an organic light-emitting diode using a 7E -conjugated polymer emissive layer sandwiched between two semitransparent electrodes: an optically thin gold film anode, whereas the cathode was in the form of an optically thick aluminum (Al) film with patterned periodic subwavelength two-dimensional hole array that showed anomalous transmission in the spectral range of the polymer photoluminescence band. At similar current densities, we obtained a sevenfold electroluminescence efficiency enhancement with the patterned Al device compared with a control device based on un-perforated Al electrode.
In the article “Deposition of an Al Cathode for an OLED by Using Low-Damage Sputtering Method” (Sang-Mo Kim, Kyung-Hwan Kim, and Min-Jong Keum, Journal of the Korean Physical Society, Vol. 51, No. 3, pp. 1023-1026, September 2007), Al thin films for OLED devices were deposited on glass substrates and on a cell (LiF/EML/HTL/bottom electrode, ITO thin film) for various working gas such as Ar, Kr and mixed gases, and various working gas pressures. The film thickness and the crystallographic and electrical properties of the Al thin film were measured by an a-step profiler (TENCOR), an X-ray diffracto-meter (XRD, RIGAKU), a four-point probe (CHANGMIN) and an atomic force microscope (AFM), and the I-V curve of the Al/cell was measured by using a semiconductor parameter measurement (HP4156A). The crystallinity and resistivity of Al thin films prepared on glass indicated that the films were amorphous with resistivities under 10−5 Ω-cm. In the case of the Al thin films deposited on cell using pure Ar or Kr, the leakage-current density of the Al/cell was about 10−4 mA/cm2, and the leakage-current density of the Al/cell prepared by using Ar and Kr mixed gas was about 10 −6 mA/cm2.
The performance of organic light emitting device (OLED) structures, based on identically fabricated Alq 3/TPD active regions, with various anode and cathode electrode structures were compared by H. Mu et al. in “A comparative study of electrode effects on the electrical and luminescent characteristics of Alq 3/TPD OLED: Improvements due to conductive polymer (PEDOT) anode” (Journal of Luminescence, Vol. 126, pp. 225-229, (2007)), and performance differences related to the different anode structure . The best performance was achieved with a conductive polymer, 3,4-polyethylenedioxythiopene-polystyrenesultonate (PEDOT), used as an anode layer, yielding a brightness of 1720 cd/m2 at 25V, a turn-on voltage of 3V, and electroluminescence (EL) efficiency and external quantum efficiency of 8.2 cd/A and 2%, respectively, at a brightness of 100 cd/m 2 and 5V.
In the article “Origin of damages in OLED from Al top electrode deposition by DC magnetron sputtering” (Organic Electronics, Vol. 11, pp. 322-331, (2010)), Tae Hyun Gil et al. examine organic light emitting diodes (OLEDs) having Al top electrodes deposited on organic layers by direct-current magnetron sputtering. The OLEDs consisted of electronically doped transport layers and phosphorescent emission layer were characterized by typical current—voltage—luminance measurement. They showed higher leakage currents, decreased forward currents, and corresponding increases of driving voltage after the sputter deposition on the organic layers. The OLEDs exhibited randomly distributed bright spots on the active area, and the bright spots were investigated by scanning electron microscopy/energy-dispersive X-ray spectroscopy. In order to prove the origins of sputter damage, simple organic/Al layer samples were made and investigated by ellipsometry and laser-induced desorption/ionization time-of-flight mass spectrometry.
Glyn J. Reynolds et al. fabricated simple thin-film capacitor stacks from sputter-deposited doped barium titanate dielectric films with sputtered Pt and/or Ni electrodes and electrically characterized (“Electrical Properties of Thin-Film Capacitors Fabricated Using High Temperature Sputtered Modified Barium Titanate”, Materials, Vol. 5, pp. 644-660, (2012)). Here, Glyn J. Reynolds et al. reported small signal, low frequency capacitance and parallel resistance data measured as a function of applied DC bias, polarization versus applied electric field strength and DC load/unload experiments. These capacitors exhibited significant leakage (in the range 8-210 μA/cm2) and dielectric loss. Measured breakdown strength for the sputtered doped barium titanate films was in the range 200 kV/cm−2 MV/cm. For all devices tested, Glyn J. Reynolds et al. observed clear evidence for dielectric saturation at applied electric field strengths above 100 kV/cm: saturated polarization was in the range 8-15 μC/cm2. When cycled under DC conditions, the maximum energy density measured for any of the capacitors tested by Glyn J. Reynolds et al. was ˜4.7×10−2W-h/liter based solely on the volume of the dielectric material. This corresponds to a specific energy of ˜8×10−3 W-h/kg, again calculated on a dielectric-only basis. These results are compared to those reported by other authors and a simple theoretical treatment provided that quantifies the maximum energy that can be stored in these and similar devices as a function of dielectric strength and saturation polarization. Finally, Glyn J. Reynolds et al. developed a predictive model to provide guidance on how to tailor the relative permittivities of high-k dielectrics in order to optimize their energy storage capacities.
According to Donna M. Joyce et al., Electrostatic capacitors offer higher power density, lower loss, and higher operating voltage than their electrolytic and super-capacitor counterparts (“Re-engineering the Polymer Capacitor, Layer by Layer”, Adv. Energy Mater., 1600676, (2016)). However, these capacitors suffer from the low energy density (<2 J cm −3), limiting their applications in high power integrated systems such as pulsed power and high frequency inverters. Donna M. Joyce et al. propose a novel approach to achieve higher energy densities by re-engineering the architecture of capacitors. The new capacitor device is a layered structure that incorporates thin electron and hole blocking layers deposited between the conducting electrodes and the dielectric material.
The quality of electrodes plays an extremely important role in all listed electronic devices. An important characteristic of electrodes is an ability to prevent considerable leakage currents. In particular, this property (quality) of electrodes is important for energy storage devices. In the electric-power industry super-capacitors are often used as energy storage devices. An increase in voltage on the electrodes of a capacitor (e.g., a super-capacitor) leads to increasing of the storage energy. The maximum value of working voltage is limited to a breakdown voltage of the capacitor. In turn, the breakdown voltage is affected by the quality of dielectric and, in particular, the degree to which the electrodes do not inject electrons or holes from electrodes and consequently do not provoke a breakdown of the dielectric of the capacitor.